1. Field of the Invention
The invention is generally in the field of hydraulic cements used in the manufacture of concrete, such as Portland-type cements.
2. Relevant Technology
In modern concrete, Supplementary Cementing Materials (SCMs), such as fly ash, slag, natural pozzolans, and limestone, are sometimes used to replace a portion of Portland cement. SCMs can yield improved concrete with higher durability, lower chloride permeability, reduced creep, increased resistance to chemical attack, lower cost, and reduced environmental impact. Fly ash and other pozzolans react with excess calcium hydroxide released during hydration of Portland cement but can retard strength development.
Portland cement is the most expensive component of concrete and contributes an estimated 5-7% of all manmade CO2. There is a long-felt, but unmet need to reduce Portland cement consumption. There are academic conferences dedicated to the concept of replacing Portland cement with SCMs. Despite an oversupply of low cost SCMs, the industry has failed to overcome technical hurdles to more effectively utilizing such materials. The failure, after decades of research and discussion, to fully utilize readily available and less expensive waste SCMs to reduce Portland cement consumption, even though doing so would reduce cost and benefit the environment, means that conventional practices for utilizing SCMs are inadequate. Hundreds of millions of tons of excess waste SCMs such as fly ash continue to be discarded into the environment worldwide each year at a cost to the producer and even greater cost to the environment.
In general, cement manufacturers deliberately produce cement having a broad particle size distribution (PSD) to create better packing between the cement particles, decrease interparticulate spacing, increase cement paste density and strength, improve flowability, and reduce autogenous shrinkage.